As one of electrical storage devices represented, for example, by a lithium ion secondary battery, a lithium ion capacitor, and an electrical double layer capacitor, an electrical double layer capacitor having the structure as disclosed in Patent Document 1 has been known. This electrical double layer capacitor has end surface electrodes (sprayed end surface electrodes) formed by a method, such as plasma spraying or arc spraying, on end surfaces of a laminate formed by laminating collectors, polarizable electrodes, and separators (for example, see FIG. 3 of Patent Document 1).
In addition, as a related laminate-type storage battery, a laminate-type battery having the structure as disclosed in Patent Document 2 has been proposed. This laminate-type battery has end surface electrodes formed by one of plating, baking, and a thin film forming method, such as deposition or sputtering, on end surfaces of a laminate in which positive electrodes each formed by arranging positive electrode materials on a collector metal film and negative electrodes each formed by arranging negative electrode materials on a collector metal film are laminated and integrated to each other with high molecular weight films (separators) which are each impregnated with an electrolyte and which are interposed between the positive electrodes and the negative electrodes (see FIGS. 1 and 2 of Patent Document 2).
However, in the case of the electrical double layer capacitor disclosed in the above Patent Document 1, the collectors, the polarizable electrodes, and the separators, which collectively form the laminate, are laminated to each other while being not adhered to each other, and when the sprayed end surface electrodes are formed on the end surfaces of the laminate as described above, the following problems may arise.
(a) Since the individual layers including the collectors, the polarizable electrodes, and the separators are not adhered to each other, and the layers in the vicinity of the end surface of the laminate are liable to be moved and deformed, kinetic energy of sprayed particles is absorbed, for example, by the movement and the deformation of the individual layers. Hence, even when colliding against the end surface of the laminate, the sprayed particles are suppressed from intruding into the laminate and being deformed, and as a result, a tight bond of the sprayed particles to the end surface of the laminate by an anchor effect cannot be expected.
(b) In order to increase the bond strength of the sprayed particles to the end surface of the laminate, when the kinetic energy of the sprayed particles is increased, the sprayed particles may enter gaps between constituent members of the laminate in some cases, and thereby the shape of the end surface of the laminate is destroyed. Hence, as a result, a sprayed end surface electrode preferable for the end surface of the laminate is difficult to form.
(c) Since there are gaps between the individual layers, the sprayed particles enter the gaps and may be short-circuited with internal electrodes (positive electrodes or negative electrodes) functioning as counter electrodes in some cases. That is, according to Patent Document 1, although spacers are provided so as to prevent a short circuit with the positive electrode and the negative electrode, the spacers each cover only an end surface portion of the electrode (see FIG. 3 of patent document 1), and the sprayed particles may enter through gaps between the spacers and the separators and may come into contact with the polarizable electrode layers to cause a short circuit in some cases.
(d) In order to arrange the spacers after the laminate is formed, a complicated process is required, and as a result, an increase in cost may occur.
In addition, in the case of the laminate-type battery disclosed in the above Patent Document 2, the end surface electrode formed by one of plating, baking, and a thin film forming method, such as deposition or sputtering, has the following problems.
(a) Since having a small thickness, the end surface electrode formed by a method, such as plating, deposition, or sputtering, is liable to be broken by a stress generated by expansion and contraction of the laminate, and the reliability is low.
(b) When the thin end surface electrode formed by a method, such as plating, deposition, or sputtering, is connected to a lead terminal or a package land by a welding or ultrasonic bonding, which is a bonding method to secure a bond having a low resistance and a high reliability, in the case of the welding, welding defects may occur in some cases since the amount of a metal necessary for welding cannot be secured, and in the case of the ultrasonic welding, since the film may be broken by ultrasonic vibration in some cases, welding having a sufficiently high reliability is difficult to obtain.
(c) Furthermore, when the end surface electrode is formed by a baking method, a binder and the like contained in the laminate may be deteriorated by heat, and as a result, the electrical properties may not be obtained in some cases.
Patent Document 1: Japanese Unexamined Patent Application Publication No. S59-048917
Patent Document 2: Japanese Unexamined Patent Application Publication No. H06-231796